Fatso. Pig. As schoolyard taunts, they're some of the worst. Implying sloth and gluttony, indulgence and selfishness, they are heavily loaded, evoking far more than a purely physical state. Characters in novels likewise take on particular traits, often negative, when they're described as fat. Piggy in Lord of the Flies is a classic example, as is Roger Micheldene, the anti-hero of Kingsley Amis' One Fat Englishman. Peter Carey's short story The Fat Man in History depicts a world where obesity has been decreed reactionary and anti-social.
Like it or not, value judgments about being physically big have firmly planted themselves in our minds. As a society, there's an opprobrium associated with being overweight, especially if extreme.
''It's regarded as a moral failing,'' says author Lionel Shriver. ''The trouble with the obesity thing is there's an assumption it's something you can control.''
Assumptions about large people abound. They feed the billion-dollar weight-loss industry, justify the belittling, body shaming of contestants on shows such as The Biggest Loser, and spur the churning out of another ''no risk, foolproof diet'' every other week.
Shriver, who is appearing at a Wheeler Centre event in Melbourne next week, still has to check herself when she goes to use the word fat. While being interviewed about her latest novel, Big Brother, on radio in the US last year, she described someone as fat and ''had her head taken off''. The experience traumatised her, to the extent that six months on she has a moment's hesitation when using it. ''Personally I want to defend my right to use the word fat. I think it's a great word - it's short and punchy and it's biologically accurate regarding the substance in your body that exists to excess when you are very large. [But] I start going for 'large' people or 'big' people or 'heavy' people just to cover myself, to make sure I don't put my foot in my mouth.''
Released last year, Big Brother centres around Pandora, whose brother Edison arrives for his first visit in more than four years, having gained hundreds of pounds. He is barely recognisable. The novel traces his family's efforts to deal with the new reality they are facing. No one can talk about the problem, but it's an unavoidable truth that affects decision-making every day, from which chairs are big enough to hold his body mass to how to keep the pantry stocked with enough food for the enormous meals he creates.
In 2009, Shriver's brother, Greg, died, aged 55, from obesity-related complications; he weighed nearly 180 kilograms. Even when it was clear his weight was significantly debilitating, she says it was not a topic they discussed: ''The only conversation I had with my brother [about it] was when he brought it up. He gave me permission to talk about it.''
Shriver is no stranger to controversy; she regularly confronts complex, polarising issues. Her novel We Need to Talk About Kevin dealt with decidedly difficult subject matter: a mother with little or no maternal feeling for her son, and a son who subsequently grows up to be a shooter of the Columbine High variety. The outsider theme is revisited in Big Brother. She gets inside the heads of those who sit outside the norms of society and examines how that reality affects the individual and their world view, as well as those around them.
That Shriver was rattled by the accusations levelled at her for using the word ''fat'' is telling. ''I also resist solving any kind of prejudice with language and euphemism,'' she says. ''I am constitutionally oblivious to that kind of thing so that means it's gotten to me.''
Of course, size is, or has become, political. ''Weight diversity groups'' advocate ''fat acceptance'' and the ''fat pride community'' is a significant lobby group in the United States. According to Shriver, doctors in Britain have been advised not to tell their patients they're obese because they might hurt their feelings.
''We've come to oversignify weight. It's one of the main things that we take in when we meet someone,'' she says. ''And … that comes with a whole set of assumptions that may or may not have any validity.''
One of the strangest things about this day and age, according to Shriver, is how much your size counts. ''It has more to do with status than it ever has before. A lot of anorexia has to do with wanting to be at the top of the totem pole. Girls, and women as well, are incredibly competitive about who is thinner. They care more about who's thinner than who's smarter, or getting into a good university. It's the thinner thing that gets them more than anything.''
Part of the obsession with what we look like may be attributed to technology. Thanks to mobile phones, photographs are taken far more easily than ever before, and social media allows their instant dissemination on a huge scale. ''The fact that we have images of ourselves more than ever before is socially and psychologically regressive. I don't understand why we would be becoming more obsessed with appearance.''
Shriver argues that in the past you didn't see yourself very often. ''It used to be via mirrors but now we have a different kind of mirror and there's something about the photograph that is sharper. It shoves up reality in our face more aggressively … There's something about looking in a mirror that you can kind of round up. Once it's objectified in that photograph, you can't lie to yourself as well. And therefore it's very easy to get sucked into trying to make that image as perfect as possible.''
So where is it going to end up? There is little doubt that the issue is accelerating. It's almost the preoccupation of our age, the irony of which is not lost on Shriver: ''On the one hand we've become more and more judgmental about our size, and yet we've got the burgeoning obesity thing.
''It's downright weird that we have magazines that are airbrushing models who are already cadaverous, shaving off their contours to the point where if they were actually that way in real life they wouldn't have room for their internal organs. The ideal does nothing but get smaller but the reality does nothing but get bigger. That's just a formula for widespread neurosis - which we've got.''
Since the dawn of time, we have been obsessed with food as an issue of survival. In the Western world today we live in an age of plenty and ''we're surrounded by it'', which Shriver argues is biologically perverse. ''We're forcing ourselves to do something that isn't natural. Animals who survive in the world when they see food, they eat it, because they're not sure if they're going to have any later. Now we have to have what is essentially unnatural discipline, a different level of consciousness, which I don't think our bodies are designed for.''
Shriver exhorts us to get some perspective and keep things real. ''We all have to start exercising a sense of mental proportion. It has to do with a kind of mindfulness,'' she says. ''[Realising] I've just wasted half an hour wondering about what to eat or feeling guilty because of what I did eat … all that stuff in your head is just junk, it's a waste - you'd be better off watching television.''
She concedes that may be easier said than done. ''Absolutism is far easier than moderation,'' she says. ''Moderation is exhausting.''
■ Lionel Shriver appears at Deakin Edge, Federation Square, for the Wheeler Centre on February 25 at 6.30pm. wheelercentre.com